Non-volatile charge-trap memory characteristics with low-temperature atomic layer deposited HfO2-x charge-trap layer and interfacial tunneling oxide formed by UV/ozone treatment

Abstract

Non-volatile charge-trap memory characteristics were investigated in the thin-film transistors with an indium-gallium-zinc oxide channel and an oxygen-deficient hafnium oxide (HfO2-x) charge-trap layer de-posited by atomic layer deposition (ALD). The HfO2-x charge-trap layer was subsequently UV/ozone treated to convert its surface to more insulating tunneling oxide. The HfO2-x charge-trap layer deposited at a low temperature of 50 degrees C was found to have a high defect density to store electrons with an areal density of 1.57 x 1012 cm-2 calculated from the threshold voltage (VT) shift of 30 V. The VT shifted positively as a result of electron charging in the charge-trap layer by applying positive gate bias, and then reduced back re-versibly by applying negative bias. Also, the shifted VT is retained over time, rendering non-volatile memory characteristics. The improved reliability of charge storage is expected to come from eliminating trap states at the interface by UV/ozone treatment. It also simplifies the overall fabrication process by removing ad-ditional processing steps of tunneling oxide layer deposition. The proposed device turned out to have a large memory window thanks to the high trap density in the HfO2-x charge-trap layer deposited by low -tem-perature ALD and the good non-volatility by using UV/ozone treatment.(c) 2023 Elsevier B.V. All rights reserved.